Molecular fossils in reefal carbonates and sponges of the deep fore reef of Mayotte and Mohéli, Comoro Islands, western Indian Ocean

IF 1.8 3区 地球科学 Q1 GEOLOGY
Facies Pub Date : 2023-12-19 DOI:10.1007/s10347-023-00678-3
Joely Marie Maak, Daniel Birgel, Joachim Reitner, Eberhard Gischler, Wolf-Christian Dullo, William J. Foster, Jörn Peckmann
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引用次数: 0

Abstract

Microbial carbonates are common components of Quaternary tropical coral reefs. Previous studies revealed that sulfate-reducing bacteria trigger microbial carbonate precipitation in supposedly cryptic reef environments. Here, using petrography, lipid biomarker analysis, and stable isotope data, we aim to understand the formation mechanism of microbial carbonate enclosed in deep fore reef limestones from Mayotte and Mohéli, Comoro Islands, which differ from other reefal microbial carbonates in that they contain less microbial carbonate and are dominated by numerous sponges. To discern sponge-derived lipids from lipids enclosed in microbial carbonate, lipid biomarker inventories of diverse sponges from the Mayotte and Mohéli reef systems were examined. Abundant peloidal, laminated, and clotted textures point to a microbial origin of the authigenic carbonates, which is supported by ample amounts of mono-O-alkyl glycerol monoethers (MAGEs) and terminally branched fatty acids; both groups of compounds are attributed to sulfate-reducing bacteria. Sponges revealed a greater variety of alkyl chains in MAGEs, including new, previously unknown, mid-chain monomethyl- and dimethyl-branched MAGEs, suggesting a diverse community of sulfate reducers different from the sulfate-reducers favoring microbialite formation. Aside from biomarkers specific for sulfate-reducing bacteria, lipids attributed to demosponges (i.e., demospongic acids) are also present in some of the sponges and the reefal carbonates. Fatty acids attributed to demosponges show a higher diversity and a higher proportion in microbial carbonate compared to sponge tissue. Such pattern reflects significant taphonomic bias associated with the preservation of demospongic acids, with preservation apparently favored by carbonate authigenesis.

Abstract Image

西印度洋科摩罗群岛马约特岛和莫埃利岛深礁碳酸盐和海绵中的分子化石
微生物碳酸盐是第四纪热带珊瑚礁的常见成分。以前的研究表明,硫酸盐还原菌引发了本应隐蔽的珊瑚礁环境中的微生物碳酸盐沉淀。在这里,我们利用岩相学、脂质生物标志物分析和稳定同位素数据,旨在了解科摩罗群岛马约特岛和莫埃利岛深海前礁灰岩中微生物碳酸盐的形成机制,这些灰岩与其他珊瑚礁微生物碳酸盐不同,它们含有较少的微生物碳酸盐,并且以大量海绵为主。为了区分海绵衍生脂质和微生物碳酸盐中的脂质,研究人员对马约特岛和莫埃利岛珊瑚礁系统中各种海绵的脂质生物标志物进行了研究。大量的球状、层状和凝块状纹理表明,自生碳酸盐来源于微生物,大量的单O-烷基甘油单醚(MAGEs)和末端支链脂肪酸也证明了这一点;这两类化合物都是硫酸盐还原细菌的产物。海绵揭示了 MAGEs 中更多种类的烷基链,包括新的、以前未知的中链单甲基和二甲基支链 MAGEs,这表明硫酸盐还原菌群落的多样性不同于有利于微生物岩形成的硫酸盐还原菌群落。除了硫酸盐还原菌特有的生物标志物外,一些海绵和珊瑚礁碳酸盐中还存在去骨海绵的脂质(即去骨海绵酸)。与海绵组织相比,去骨海绵的脂肪酸在微生物碳酸盐中显示出更高的多样性和更高的比例。这种模式反映了与脱螺旋体酸的保存有关的重要的造岩学偏向,碳酸盐的自生作用显然有利于脱螺旋体酸的保存。
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来源期刊
Facies
Facies 地学-地质学
CiteScore
3.70
自引率
5.60%
发文量
15
审稿时长
>12 weeks
期刊介绍: The journal is open to papers dealing with the interpretation of ancient and modern biotopes and carbonate depositional environments by means of facies analysis in its broadest sense. Once the central part of research in hydrocarbon exploration, facies analysis more and more integrates modern and ancient biogeological processes of a changing earth. Special emphasis is laid on paleobiology and -ecology, basin evolution, sedimentology including diagenesis and geochemistry, as well as studies emphasising the impact of life on earth history. The main part of the target group will be people in academia.
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